Control terminal for mobile radio telephone



Nov. 20, 1951 E. H. B. BARTELINK 2,

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CONTROL TERMINAL FOR MQBILE RADIO TELEPHONE Filed Dec. 18, 1948 9 Sheets-Sheet 8 OUTPUT DECIBELS Q h wlr l.

INVENTOR. EVERHARD H. B. BARTEILINK. l v BY may M ATTORNEYS.

E. H. B. BARTE LINK 2,575,782 CONTROL TERMINAL FOR MOBILE RADIO TELEPHONE 9 Sheets-Sheet 9 Nov. 20, 1951 Filed Dec. 18. 1948 EVERHARD H. B. BARTELINK.

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Patented Nov. 20, 1951 CONTROL TERMINAL FOR MOBILEfiADIO' TELEPHONE Everhard H. B. Bartelink, Bronxv'ille, N.,Y., as-

signor, by mesne assignments, to Automatic Electric Laboratories, Inc., Chicago, 1 11., a corporation of Delaware ApplicationDecem-berm, 1948,Seria1No. 66,010

17 Claims.

This invention pertains to mobile radio telephone systems in which a multiplicity of mobile subscribers telephone stations are linked by radio to land-based, i. e. permanently located, radio transmitting and receiving stations, which latter are connected over land-based wire lines, 1. e. metallic circuits, to a control terminal, and thence to a central office or toll switchboard, whereby ther nobile stations may communicate with landbased subscribers stations and also with each other.

The present invention pertains more particularly to the control terminal and appurtenant portions of such a system, including the circuits from the control terminal to the central office and the land-lines extending between the control terminal and the land-based radio transmitting and receiving stations, and provides equipment for such purposes, of a new design characterized by various novel features of circuit arrangement and operation, described in detail hereinafter.

This application is a continuation-in-part of my co-pending application on the same subiect, Serial No. 741,289, filed August 14, 1947, now forfeited. 4

The broad purpose of a mobile radio telephone system is to extend telephone service to subscribers stations located on mobile units as trains,- planes, automobiles, ships, etc., and thereby enable occupants therein to coi'r'ini" cate by radio with the centre-rents, afidfthence over land-based facilities with any land b'ased subscriber served by such facilities, or by radio with other mobile stations. To thiserid, the mobile stations are provided withiadio "trails mitter and receiver units; andpreierably also with station selectors responsive todialing'ipulse's, whereby the central ofi'lce operator may dial any mobile station desired. Station selector 'cire cuits appropriate for this purpose are described in my co-pending applications Serial No. 729,828, filed February 20, 1947, now abandoned, and Serial No. 20,719, filed April 13,1948, now Patent No. 2,478,361.

The control terminal serves the functions of connecting the land-based radio transmitter and receiver units of amobile radio telephone systern with each other and with the central office switchboard, andof providing the necessary 'supervision signals for the switchboard operator at the central ofiice, and also for the technical operator at the control terminal. In addition it permits the technical operator at the control mobile subscribers stations are much lower in power output in order to be economical. their range is smaller than that of the main transmitter coverage. Accordingly, a numbenof land-based radio receivers are ordinarily provided which are connected over two-conductor, wire lines to the control terminal, these landbased receivers being strate ically located throughout the service area in such arrangement that at least one such receiver will always be within easy transmitting range of a mobile station, irrespective of the latters particular location in theservic'e area. A A

The control terminal comprises a control panel which interconnects all units aforesaid and controls their functions, via, land-based transmitter and receiver units and the central office, and additionally comprises to this end, at least one land-based radio transmitterline panel and at least one land-based radio receiver line panel, together with a limiting amplifier panel which also contains a transfer relay for disconnecting the limiting amplifier during dialing, and also one or more toneoscillators, which generate the dial tones, together with pulsing relays which modulate'or interrupt the same under control of the dialing equipment at the central ofiice and at a technical operators position on the control terminal.

The control terminal is also equipped with provided in the control terminal permits the technical operator to monitor all transmissions whether they are controlled from the switchboard or from the control terminal.

It is desirable thata reasonably constant modulation level be applied to the land-based radio transmitter, and, to this end, the control terminal contains the above mentioned limiting amplifier which is connected in the outgoing metallic circuit to the land-based transmitter; l The incoming metallic circuits from the laiidbased receivers are also connected to the i npjut of the limiting amplifier to provide for intercommunicationbetween mobile stations.

The transmitter and receiver line pan l in.

clude attenuators for setting the proper transmission levels outgoing to and incoming from the land-based transmitter and receiver units, and are further equipped to transmit supervision signals to and from the land-based transmitter andreceiver units.

1 when the outgoing carrier of the land-based Thus Patching and monitoring jacks are also provided in these units,

transmitter is switched on, and when incoming carrier is being received by one of the landbased receiving units. In the case of the landbased receivers, facilities are provided on the receiver line panel at the control terminal, for complete switchover from a normally used landbased receiver to a stand by receiver. If more than one land-based receiver is normally employed, as is ordinarily the case, a corresponding number of receiver line panels are provided at the control terminal; and, in this case, these panels are equipped to provide an extremely simple type of signal-to-noise ratio selections between the various land-based receivers.

An off-frequency alarm is provided at the control terminal and at the central office operators switchboard position, which will alert the central oflice and technical operators, whenever the land-based radio transmitter is not operating on the proper frequency. Separate provisions in the control terminal permit the addition of an east-west busy indication where the mobile system operates as part of a chain of highway stations having overlapping coverages.

The control terminal of the invention performs in general the following functions: On incoming calls this unit will light a call lamp at the central office switchboard operators position, to alert the switchboard operator as soon as a mobile subscriber has lifted his handset and pressed his push-to-talk button. When the operator answers the call by inserting her cord plug into the switchboard jack over which the call is incoming, the call lamp is extinguished and a busy lamp lighted, which remains lighted as long as the operators cord is inserted.

On outgoing calls, the control terminal will connect a tone oscillator to the land-based radio transmitter, as soon as the central ofiice operator has inserted her cord plug into the appropriate switchboard jack. Circuits are then provided which will permit the operator to dial mobile units equipped with selective calling systems, by means of her regular switchboard dialin equipment. In this connection the control terminal of the invention is designed to permit the dialing into mobile units equipped with either the well known Western Electric 106A type of selector system, and also the dialing of mobile units equipped with selector systems in accordance with those of my co-pending applications Serial Nos. 729,828 and 20,719 aforesaid.

The control terminal of the invention will maintain the dial tone connected to the land-based radio transmitter for a short period after the last digit has been dialed, in order to provide ringing in the le unit. The busy lamp is lighted on outgoing calls as soon as the operator has plugged her cord into the switchboard jack, and remains lighted as long as her cord plug is thus inserted.

Disconnect signals are obtained from the wire line subscribers circuit on calls between mobile and wire line stations, and appear in normal fashion in the operators cord circuit as soon as the wire line subscriber hangs up.

The control terminal of the invention is also arranged to provide for conversations between mobile units. In such cases the operator upon receiving the number of the desired station to be called, must remove her cord circuit plug from the mobile service jack, and reinsert the same, and thereupon dial the desired mobile unit number as soon as the calling party has released the push-to-talk button. When the called party answers, the operator will notify both parties to proceed with their conversation.

The system of the invention is characterized by the following features: Whenever the operator originates a call, a dial tone is applied to the'line. Whenever an operator answers a call, no dial tone is applied. The dial tone persists for an adjustable period of time after the operator plugs in a cord. This period is called the tone-delay period. If dial pulses are transmitted, the tone delay is rejuvenated on every pulse so that the dial tone persists for the tonedelay period after the last dial pulse of any dial operation. The transmitter is under the control of a slow-acting relay and remains energized during the dial pulses. The transmitter relay is controlled by one of the dial loop supervision relay contacts. Incoming calls lock up the line relay, .which keeps the line lamp lighted until both the transmitter and the monitorreceiver relay have operated.

Tone delays are obtained by means of a vibrating relay, or other delay relay, which in turn keeps a super-slow relay energized. The latter can be a regular slow-release relay. The vibrating or other delay relay can only be energized when the line relay is unenergized, the monitor relay is in the system idle position, and the dial loop supervision relay energized. Once the vibrating or other delay relay is energized and ha in turn energized the super-slow relay, a new energizing circuit is formed through a spacing contact of the line relay, a contact on the monitor relay which is made when the main transmitter is in operation, and a contact on the loop supervision relay which is made when the loop is interrupted by dial pulses.

For resetting some selectors, such as the Western Electric Companys type 106A, two

extra relays are provided which cause a short interruption in the ground lead controlling the tone oscillator shortly after it has been energized and shortly before the transfer relay releases.

The tone oscillator is controlled by a contact in the dial loop supervision relay. Application of ground to this lead applies the tone, and interruptions of this ground lead interrupts the tone for mobile units equipped with station selectors in accordance with my applications aforesaid; while application of ground switches in tone, and interruption of ground switches the tone oscillator to another frequency for mobile stations equipped with other types of selector systems such 'as the Western Electric Companys 106A. The super-slow relay applies ground to a lead controlling the transfer relay which transfers the voice circuit leading to the transmitter from the receiver and line circuits to the tone oscillator output. Simultaneously, this transfer relay applies the tone to the line circuit through an attenuator to give start dialing supervision to the central ofiice operator.

More than one tone oscillator can be controlled by this control panel, provided two different jacks are installed on the switchboard and connected in such a way that insertion of a cord in one jack operates a relay, transferring the system from one tone oscillator to the other.

In the drawings:

Figure l is a block diagram layout of a mobile radio telephone system of the character to which the present invention is applicable, this figure illustrating the circuits and apparatus employed ants- 2 it forestablishing a connectiomfrom a mobile subscribers station to a land-based subscribers station; while Figure ,2 is a diagrammatic layout of the essential components of a mobile subscribers telephone station.

Figure 3 shows the basic circuit arrangement of the line termination panel which, when wired in accordance with the various options A to D inc., illustrated in Figure 4, and option E illustrated in Figure 8, is employed to terminate both the control terminal and the distant ends of the two-wire metallic circuit which extends from the control terminal to the remote landbased radio transmitter, and which is also employed to terminate both the control terminal and distant ends of each of the two-wire metallic circuits extending from the control terminal to each of the remote, land-based radio receivers of the mobile radio system. Figure 4 illustrates the option board on which the wiring connections for the various options aforesaid are made, and further illustrates the wiring connections for options A to D aforesaid, while Figure 8 shows a further option E as referred 'to below.

Figure 5 is a wiring diagram of the two-wire metallic circuit extending from the control terminal to the remoteland-based radio transmitter, including the line termination panels at each end thereof, .as wired respectively in accordance with options B and D of Figure 4.

Figure 6 is a wiring diagram of the two-wire metallic circuit extending from the control terminal to a remote, land-based radio receiver including the line termination panels at the control terminal and distant ends thereof as units are connectible to an antenna [8 through contacts of a relay I9, actuatable by a handset push-to-talk button 26, thereby to switch the antenna [8 from the receiver input to the transmitter output.

The mobile station is linkedby radio, as indicated at 2!, 22 to a land-based transmitter T, and land-based receivers, such as R-l, R-2, lit-3, etc. As stated, the land-based transmitter T is sufiiciently powerful to serve all mobile stations within a preselected service area. On the other hand, the mobile station transmitters such as l2, are of much lower power output in order to be economical. Accordingly, a multiplicity of land-based receivers are strategically located throughout the service area, so that at least one of them, such as R -l, R-2, R-3,etc., in the drawing, will be within easy transmitting range of the mobile station MS, irrespective of its location in the service area.

The land-based transmitter T and receivers R-l, R-2, R-t, etc., are connected over wire circuits such as 23 to 25 inc., to a control terminal 21, where they are connected in the manner above referred to and as indicated at 28 over awire circuit 29 to a toll switchboard so, from whence a connection may be completed from the mobile station to a land-based subscribers station, such as 3|, overa toll line circuit 32- and through a central offlce 33, to which the laifldbased subscribers station 3| is permanently connected.

Each land-based receiver R-l, R-2, etc., is provided with a carrier current actuated relay C, commonly referred to as a Codan relay, at least one of which, i. e., that nearest the mobile station MS, will be actuated upon receipt of incoming carrier 22 therefrom, thereby to actuate a calllamp wired respectively in accordance with Options A and C of Figure 4.- a a a Figure -7 is a wiring diagram "of the control terminal end of land-based radio receiver circuits, employed where apluralityof land-based radio receivers are required; while Figure 8 illustrates modified wiring connections required on the option board of Figure 4 in conjunction with those on certain terminals of the receiver line panel, for providing the circuit arrangement of Figure "'7, the Figure "8 wiring connections being referredto herein as optionE,as above noted.

Figures!) and 10 show thewiring diagram for the overall system layout including the control terminal and circuits and apparatus appurtenant thereto, including the tone oscillators, central office switchboard, limiting amplifier and the land-based transmitter and receiver line panels at the control terminal ends of the circuits 'extending to the remote land-based transmitter and also to the remote land-based receivers.

Figure 11 is the wiring diagram of the limiting amplifier above referred to; while Figure 11a illustrates graphically the input versus output gain characteristics thereof.

Figure 12 is the wiring diagram of the tone os cillator employed for dialing mobile units equipped with station selectors in accordance with my applications Serial Nos. 729,828 and 20,719 aforesaid, according to which station selection is effected by dialing interruptions of the dial tone.

Referring to the block diagram layout of Figs. 1 and 2, there is shown at the right a mobile subscribers station MS, mounted in a mobile unit such as an automobile H. The mobile sta tion com-prises a radio transmitter l2, a radio receiver 13 and a station selector i4, connected through a control panel Hi to a handset I6, normally resting on a switch hook H. The radio transmitter and receiver at the technical oper ators position, i. e., at the control terminal 21, and also at the central oflice operators position on the switchboard 30, as explained below. Some of the outgoing carrier from the land-based transmitter T is transmitted to the adjacent frequency monitor 34, which signals the control terminal over connection 35, and also the toll switchboard, and operates alarm lamp thereat, and also, if desired, a bell or buzzer, whenever the outgoing carrier from transmitter T is operating off frequency, as explained below.

On calls outgoing from the central oflice to a mobile. subscribers station, the outgoing carrier 2i from transmitter T is modulated with dialing signals, as indicated at 36, to actuate the station selector !4 at the desired mobile station, and thereupon to energize suitable signaling devices, lamps, buzzers, bells, etc., at the called station, as is fully disclosed in my aforesaid copending applications Serial Nos. 729,828 and 20,719.

Before turning to a detailed description of the overall operation of the system, with refer-= ence to the wiring diagrams thereof, certain components thereof will first be described, as this will facilitate comprehension of the overall operation. Accordingly, discussion' will first be had as to the construction and operation of the wire circuits extending from the control terminal to the remote land-based transmitter and to the remote land-based receiver or receiver units.

The general functions of these circuits are asfollews; The lines between the central office and theremote transmitter or land receivers are required to transmit voice-frequency signals in vision signals in both directions. in the case of the" land-based transmitter, a direct current sig--.

nal must be transmitted thereto in order to switch the transmitter on and off, and a direct current signal must be received therefrom at the control terminal in order to relay the indie cations of the frequency monitor into the control terminal. In the case of the land-based receivers, the operations of the Codan relay thereat must be transmitted to the control terminal over a direct current circuit. Also, it is in general advantageous to install a standby, landbased receiver and to arrange for remote switchoverfacilities, operated from the control terminal, to substitute the standby receiver for the normal receiver when necessary. This requires a further direct current signaling path from the control terminal to the land-based receiver location. When more than one land-based receiver is employed, it is desirable that the first receiver which picks up an incoming carrier, disable the other receivers. This is necessary to prevent interference from more distant receivers, that might receive a Weak and noisy signal from a mobile station.

For effecting the aforesaid voice transmission and direct current signaling operations, a basic termination circuit has been devised, in accordance with one feature of the invention, the wiring diagram of which is shown in Fig. 3, which basic circuit may be wired on an associated option board 0, in accordance with the various strapping connections illustrated as options A to D, inclusive, of Fig. 4, and option E of Fig. 8, for appropriately terminating the control terminal and distant ends of the two-conductor metallic circuits extending from the control terminal to the land-based transmitter and to the land-based receiver units respectively.

Referring to Fig. 3, this basic circuit comprises a four-winding, iron core transformer F, having the inner and outer terminals for each winding brought out, a pair of windings 40, 4| having their inner terminals strapped as at 42 and their outer terminals normally connected respectively through a T-type attenuator pad 43 and contacts of a switch S! to a pair of terminals T-3, T-4. When switch 8-! is actuated, the upper connection from the attenuator 43 to terminal 'I -3 is opened, and in substitution therefore, a line terminating resistance 44 of, for example, 600 ohms is bridged between terminals T-3, T-4; while a similar line termination resistance 44a is bridged across the attenuator 43. The remaining pair of transformer windings 45, 46 are connected together at their inner terminals through a condenser 41, their outer terminals extending respectively over connections 48, 49 and through circuit-breaking jacks 50, 5| to a pair of terminals T-I, T-2. Bridged across condenser 41 is a connection which includes in series a line relay L and another condenser 52. These condensers isolate the upper and lower conductors 48, 49 to provide separate direct current signaling circuits as above mentioned and explained below; while the transformer F isolates the voice circuit. The basic circuit also includes an option board having terminal lugs I to ID inc. thereon, and also includes various connections extending from the terminal lugs of the option board to other terminalssuch as T-G, T-l, etc., the significance of which will become aparent from subsequent discussion thereof. The line relay L has various contacts L-l to L-3 inc., connected to various other terminals, such as T-B,

8.. T-l2, T-| 5,. etc; for purposes; to beiexplairie'd. The circuit also. includes a pilotlamp 53 and a switch 5-2 for purposes, explainedbelow; also a monitor jack-54, the latter normally connected across the attenuator pad 43 through a high re-,

sistance 5501', for example, 3000 ohms, for mon itoring purposes. When switch S-l is operated, however, the monitoring jack 54 is bridged by the line terminating resistance 44a directly across the line attenuator 43, for measuring gain levels, etc., while resistance 55 is shunted out.

Referring to Fig. 5, there is shown a two-wire metallic circuit 60, 6| extending from the control terminal CT to a land-based transmitter LT, having thereat a frequency monitor FM. Atthe control terminal the metallic circuit 60, 6l terminated in the basic terminating circuit or line panel of Fig. 3, as wired on the option board 7 0 thereof, in accordance with option A of Fig,

4; while at the land-based transmitter LT, circuit 60, BI is terminated in the basic circuit of Fig. 3 as wired on the option board 0 thereof in accordance with option D of Fig. 4. Referring to Figs. 3 and 5, various of the terminals T-l to V T-|1, inclusive, of the basic'circuit of Fig. 3, "are connected to the Fig. 5 circuit, to the control terminal CT, to the land-based transmitter LT, to the frequency monitor FM, and to the metallic circuit 60, BI, in the manner designated by the like-numbered terminalsT-l, T-Z, etc., in the Fig. 5 showing. Also in the Fig. 5 showing, the line relays, attenuator pads, transformers, etc., of the basic circuit, as employed at the control terminals and distant ends of circuit" 60, 6|, respectively, are designated L, A, F, etc., and LL, AA, FF, etc., respectively, in order to avoid confusion.

Referring now more specifically to the operation of the Fig. 5 circuit, the control terminal CT will apply battery to conductor 60, as ex-''. plained below, to the line. panel terminal T-l4 lay to operate. Operation of the LL relay will. complete, through its LL-2 contacts, a circuit to switch on the plate power relay 63 of the transmitter LT, over a circuit energized from volts alternating current supplied to the transmitter power supply terminals 64. Operation of the LL relay also completes a circuit from the frequency monitor FM at the land-based transmitter and extending to the control terminal, to indicate whether the transmitter is operating on frequency. This circuit is traced from ground at 65, through the contacts 66 of the contacting galvanometer 61 in the frequency monitor, and over connection 68 therefrom through the LL-| contacts of the LL relay, through the normally closed switch SS-Z at the transmitter, and through the lower winding 46 of the transformer FF thereat, and over conductor 6| of the metallic circuit, tothe control terminal line panel, and through the upper winding 45 of transformer F thereat, and thence through theline relay L to battery. The L relay will be en? ergized over this circuit whenever the'transmit plication ofbattery 82a to conductor 62 -at the control terminal also lights the pilot lamp 69 -in the: linepanel, through the right-hand 'contacts of toggle switchS-Z, to indicate that thetransmitter is switched on, Operation ofswitch S 2 prevents the transmitter from being switched on by an operation of the control terminal CT. ()peration of the switchS-I: interrupts the voice frequency circuit 'H- from the control terminal, andvterminates the circuit in the line terminatingyresistance 44; I as explained; It also terminates'the-metalliccircuit'60, 6|, in a corresponding terminating resistance 44a through the attenuator pad A. At the distant end, the frequency monitor may be disconnectedby operation of switch SS4. Likewise; operation of switch" SS4: disconnects the metallic circuit 80, BIsfromthe speechinput circuit to the transmitter 'LT, and substitutes therefor the line ter minating resistan'ce144a; while terminating the metallic circuit 12 in resistance-44.

Referringnow to Fig; 6, there isshownatwowire'metallic circuit 15,16, extending from the control: terminal CT to a landebased I receiver Station, at which-area located a normally used radio'receiver LBW-A" and a standby receiver LR'P-B At the" control terminal, circuit 15; 1B is terminated; in the basic terminating: circuit of 'Fig. 3; as wired on'the-option board thereof, inaccordance with optioniA-iof 'Eig. 4; while at the land-based receiver station, circuit I5, '16 is-terminatedrinthe basiccircuit of'Fig. 3 as wiredon theoption board-O in accordancewith optionC of Fig. 4;

The audio frequency output iifl of-"the normal receiver LR,A is connected to circuit 15; 16 through transformer FF over connections '8 I v and 82, the latter extending through the LL--3 back contact and armature of the LL relay, andthence through the normally closed contacts oi toggle switch SS-I. The audio frequency output 83 of the standby receiver LLR--Bis* connected to circuit 15; 16 through the FE transformer, over connections B I and 84; the latter extending through the ILL-3 front contactandarmature of the LL relay. Thus the voice output of the normal receiver LR;-A is normallyconnected to the metallic circuit I5, 16, extending to the control terminal, but upon operation of the LL relay the voice output of the standby receiver LP,B is substituted therefor. A common, co-axial antenna circuit 85 provides'the incoming radio frequency signal pickup for both the normal and standby receivers LR'A andlR -B, the antenna circuit being selectively conneetioleto either the LR--A orLR-B receivers under control of the coaxial antenna switch over'relay 86. It will be noted in this connection, that the outer sheath of the antenna cable concentric conductor is permanently connected into both receivers LR-A and LR-B as at 8?, 88 while the center conductor 89 terminates in a switch arm 90, displaceahle between upper'and lower contacts connected respectively I to the central conductors of connections Bland extending into receivers LRr-A and Lit-B,- respectively. Normally, the

'10 switch arm rests against its upper contact to connect the antenna circuit into receiver LR-A, but energization ofthe switch-over relay 86 connects theantenna to the standby receiver LR.B. Relay 85 islenergizable from a source of: socket power-supplied'to power inputterminalsSI, this cii'cuitbeing traced from the lower of terminals 9I over connection 92, through the winding of relay 86' and over connection 93; through the LL-Z front contact and armature of the LL relay, returning thence over. connection 94 to the upper power input terminal 9|. Thus, operation of the relay actuates the co-axial antenna switch over relay 88 to transfer the antenna circuit 853 from 'thevnormal or LR-Areceiverto the standby" or LRB receiver. The socket power supply' ior energizing both thenormaland standbyreceivers LRe-A and LR;B; is alsoisupplied from thepower input terminals "9 I through back 'andfront'contacts respectively, of the-antenna: switch-over relay 36; Thus the power supplycircuit for receiver LR+A is traced from the lower" power input terminal 95 over connections'92 and 95, to'the receiver power supply input"96'; returning thence: over connections? 9T1 and vim-through the'outer right back contact and armature 'ofl-relay' flfi. Thepower supply: circuit for: the 'standby receiver'LR-'B extends from the lower power 'supplyterminal9|; over connections 92 and 99, to the receiver power input terminals I 0 0, returning thence over connections IOI and 98, throughthe inner right front contact:and innerarmature ofrelay 86. Thus, op;- eration" of relay 86' switches the power supply from the normal receiver to the standby receiver LR-B. Asabove stated; a direct current signaling circuit must beprovidedover the metallic circuits"; It; to relay to the control'rterminal, operations of the Codan relay C-I or 01-2 of ithe normalor standbyreceiver LR.A or" LRr -B, whichever happensto" be in operation at any particularmoment: This direct currentsignalingcircuit for the C-I- relay extends from ground IIJ2 thereat, through contacts Ill3'of theC-I Codan-relay, thence over connection lll lrthrough the LL- I-* back contact and armature of the LL relay, through normally closed toggle switch SS 2"to the lower transformer winding: 4B= ofthe FF transformer, thence over connection 16 to the control terminal, and'through' winding 45 of the F transformer-thereat, and thence through the L relay to-. grounded'battery I05: Insomewhat similar fashion, the operating circuit of the C-2 iCodan relay ofthe standbyreoeiverextends from ground I 06* thereat, through" its op.- eratingcontacts' Illl ofthe relay 0-2 and over connection I08; and through the- LL-I front contact 'and' armature offthe LL relay, tothe toggle switch SS4, the operating circuit ex:- tending thence to thecontrol terminal 1 being the same asthat above traced for the- (ll-I relay. Accordingly; operation or the LL relaytransfers the signaling circuit for thereceiver codan' relay from the normaireceiver LR-eA to the: standby receiver-*LRQB; For switching" operations from the normal-or LR A receiver to those of the standby receiver, a remote switch-over circuit is provided whichextends from groundedbattery I I 0 at the control terminaLthrough toggleswitch S4 thereat, thence. through thelowerwinding 4-5 of the Etransfermer, and over-conductor 15 to :the receiver station, thence through the upper winding" 45 of w the; FF transformer thereat and through the: LL I relay to I ground- Thus, so long as-theitoggle switch 5-2 remains n, the

: relay will be released, to close all operating 'circuits for the normal receiver LR-A through the LL I to LL-3 armatures and back contacts of the LL relay. Operation of toggle switch 8-2, however, completes the operatin circuit above traced for the LL relay, thereby to energize the same and switch its LL-I toLL-3 armatures from their back to their front contacts, thus to substitute the standby receiver LR-B for the normal receiver LRr-A, in the various op-z cratin circuits above traced.

As above pointed out, the L relay at the con- .trol terminal will operate whenever the receiver control terminal CT itself, over a circuit 21$,v completed through the L-2 armature and front contact of the L relay, for purposes as exp ained hereinafter in connection with a description of the control terminal circuit. Operation of the L relay in response to operation of the receiver: Codan relay, also lights a call lamp H2 in the line panel at the control terminal, over'a circuit traced from battery H3 and extending through the L-I armature and front contact of the L relay, and through the call lamp II2 to ground at the control terminal or central oflice, over a connection 4 extending thereto, and as referred to hereinafter in connection with a description of the control terminal circuit operations. The speech input from circuit I5, I6 into the control terminal, extends through the transformer F and attenuator A, and toggle switch S-I, to the control terminal speech input circuit I I5.

When a mobile radio system in accordance with the invention requires a multiplicity of landbased radio receivers disposed at various points over a geographical area to be served, it is necessary to employ the circuit arrangement of Fi '7. Referring to this figure, two land-based receivers are illustrated diagrammatically at I I6, N1, the speech outputs I I8 and II 9 from which are respectively connected through line terminating circuits I20 and HI, per Fig. 3, as wired in accordance with Option C of Fig. 4, to metallic circuits I22 and I23,, extending to the control terminal CT. At the control terminal, each of the metallic circuits I22 and I23 is terminated .in -a line terminating circuit I 24, I25. per Fig. 3, as wired, however, in accordance with Option E of Fi s. 3 and 8. The audio output connections I26, I21 from the line terminating circuits are bridged across a common circuit I28, comprising the speech input circuit to the remainder of the control terminal CT. Referring, for the moment, to Fig. 8 in connection with Fig. 3, it will be noted that the option E wiring includes, in addition to the strapping connections shown on terminals I to ID of the option board 0, alsostrapping connections between panel terminals T-I and T-II, and between T- and T-I5, of the Fig. 3 circuit. In the circuit of Fig. '7, the L relay in each receiver circuit I22, I23 at the control terminal, is energized, as in the Fig. 6 arrangement, over a circuit traced from grounded battery I29, I30, through a current limiting resistance I3l; I32, thence through the L relay winding and over one of the conductors I22, I23, to ground at the receiver station through contacts of the Codan relay C-I, 0-2. However, in the Fig. 7 circ it, each That is to say, the L relay at the con- 0 of the resistors I 3|, I32 is also connected on the side away from the battery, to the L-2 back contact of the corresponding L relay, the corresponding armature of which is connected to a conductor I35, which latter extends to the winding of a call relay I36 in the control terminal, the opposite end of which winding is connected to grounded battery I3I. In addition, the L2 front contact of each of the L relays, is connected to ground as at I 38, I39. Accordingly, whenever a mobile station places a call, the land-base receiver, such as H6 or I H, which is the first to operate its Codan relay C-I or (3-2, energizes the corresponding L relay at the control terminal, the operation of which connects its L-2 armature to its grounded front contact, such as I38 or I39, which thus connects ground, overconductor I35, to the L relays of all of the other land-based receiver circuits, thereby preventing any such other L relays from operating. Thus, for example, assume that when a mobile unit places a call, it is closest to the land-based receiver station H6, and hence causes its Codan relay C-I to operate before the Codan relays of any of the other receiver stations are operated; The operation of Codan relay C-I will connect ground through its contacts to the upper conductor of the metallic circuit I22, thereby to actuate the L relay in the line terminal circuit I24 at the control terminal. Operation of this relay connects the ground at I38 to its L-2 armature, which ground connection is immediately applied over conductor I35 and through the L-2 armature and back contact of the L relay in terminal I25, to the L relay winding thereat, thus preventing any operation of this relay in response to operation of the corresponding Codan relay (3-2 at the landbased receiver 1. A selection of this character takes place upon initiation of each call from a mobile unit. Since the amount of incoming carrier of any receiver circuit is related to the quality of reception, the first receiver having its Codan relay thus energized, will probably have the least signal-to-noise ratio, and for this reason it is desirable that this receiver be selected for the incoming call, to the exclusion of all others. Thus the best receiver is automatically chosen on each call. By means of the contacts L-3 of the L relay, the speech incoming on the receiver circuit thus selected, is switched into the control terminal over its speech input circuit I28, and from whichever receiver circuit has its line relay L thus operated. Operation of the switches S-I and S-2 and the line lamps I40 and I M in the line terminating circuits I 24, I25, etc., is the same as for the Fig. 6 circuit above described.

Reference is now had to Figs. 9 and 10, which show in circuit diagram form, the overall system layout of the control panel and appurtenant apparatus in accordance with the invention. Referring to Fig. 9, the essential circuit components thus involved comprise: (a) the control panel as designated by the rectangle I52, and embodying the circuits and apparatus enclosed within the rectangle, shown in Fig. 9 in rather a simp ified form, but shown in complete Wiring diagram form in Fig. 10; (b) an oscillator panel I5I, mounting a dial tone oscillator I52 and a dialing relay PR, for dialing mobile stations equipped with station selectors in accordance with my co-pending applications 729,828 and 20,719, wherein station selection is effected by dialing pulse interruption of asingle dial tone, the wiring diagram for this oscillator circuit being shown in simplified form Within the rectangle I5I of 13 Rigs! the.complete*wiring diagram beinglshown, however, in Fig, 12, as discussed below; to) an oscillator panel I54; mounting-1a pair of dial tone oscillators I55, I56: anda; dialing" relay P, for

lector;a1l this'equipment being wel-l -kno-w nlin the I act, as. described in" the Western Electric, Come panyspatents and literatureson thesubiect, and hence requiring no. detaileddescription. herein, the essentials of the oscillator circuitior purposes. of: the present. invention being su-fliciently disclosed within the rectangleI54iaforesaid; (d) the control terminal receiver lineipanelslsuch as I5B,--l59, of one or more-llandabased receiver circults such as. Hi6, :IfiI. as wired inlaccordance' with Fig. 5 above-discussed, where-only one land? basedcneceiver circuit is employed, and as: wired in accordance with Fig; 7 above vdiscuss-ed, where morethan-onolandebased receiver. circuit is Emsployedg. (e) the control terminal transmitter line panel. 152 for the land-based transmitter circuit -I 63, ,the complete wiring. diagram of which is shown in Fig.5; :above discussed; if.) the. central ofiiceswitclrboard panel I'fi4,.illustrated as ,mou nting thenecessary switchboard jacks. 155, 156., su-

pervisory and busy lamps 1.61;, I6.6,letc., for opera.-

tion in accordance with thesysteznoi. the present invention, as discussed below; and (g), a limitingtamplifier panel 169,, mounting, a limiting, amplifier 150,. shown in simplified. form in :Fig. 9., the complete wiring diagram. of. which ,is,,how ever,. shown. in. Eig. ll, discussed. below...

Referring .still. to, Fig. 9,. the general layout of the. system is asiollowsz The voice frequency out-- put-s I11, I12' oi, the land-based receiver cit.- cuits I55, I61 are connectedin parallel to a two-Wire. metallic circuit I13, which extends through a transformer T-I toa two-wire metal? lic circuit I15, which latter-terminates at the central. ofiice' switchboardiffid, in the tip and sleeve conductors, respectively; of the operators switchboard jacks I55; I66; in multiple; To cir- I cuit' I13 there is "alsoconnected, in parallel with the receiver circuit voice-frequency outputs I1 I, [12; the audio input circuit! 15 ofthe limiting amplifier I15, the output c'ircuit I15 oi'whichds connected, through the B"-I back contact and armature of a transfer relay-B, to the voice frequency input circuit I'1'1 oi the landbasedtra'nsmittercircu'it 63. It will'beseen that with the circuit as traced thus far, speechincoming over either of the land-based receiver circuits I56, I51, will be transmitted over-circuits1i13; I1:5*to the operators switchboard jacks 165, I66; and" will also be transmitted over circuitxl 1'5' andthrough the limiting amplifier I16 to the land-based transmitter circuit' l'53, fonre transmission from the-land-based transmitter; this latterv for permittingfone mobile station to talk withanyoth'er, as discussedmore fullybelow;

As, was mentioned above; adial-jtone is applied to'the land-based transmitter on out oing alls; and interruptions I or ireql fincy, changes of this dial tone are: used to transmitdialing code,-

which will activate. the selectors;- in the mobile and operate the bell orbuzzer inthe. mobile station called; As. was also; [mentioned above, the

limiting amplifier; H0 is provided in. order to prevent over-modulation of the transmittergandto apply additional amplification to weak incoming signals such as mightbe obtained,,for1 instance,

- over a high-attenuation; toll line connected .to

one of. the switchboard ,jacks I65, I65.

Thelimiting amplifier I10 would cause serious distortion in the dial pulses obtained from the tone oscillators I52, or I55, I56. For this reason, it is necessary completely to disconnect the limit.- ingamplifier I 1!! whenever the dialing operation iscperiormed. Accordingly, the audio frequency input circuit I11 to the land-based transmitter circuit I63, is. connected to the B-I armature-of the transfer relay B, whichrelay, when de-energized, connects this armature. to the limiting amplifier output circuit H6, but-which, when ener gized, transfers the transmitter input circuit I11 to the output from one of the tone oscillator pan? els 15!, I54 over acircult I18, in the manner described below. The manner in which the trans, fer relay B is energized by circuits in the controlpanel will be discussed later. At this point, however, it is; pertinent to bringoutthat the transfer relay B is also providedwithtan additional set of contacts B-2, the functionof. which is to apply the dial tone, emanating from-one of the oscillator panels I5I, I54, to the switchboard operators jacks I65, I65, thus to inform her when the dial tone circuit selected is ready for. the start of. the dialing operation. For this purpose a T-pad' attenuator l19 is connected, as shown in Fig. 9, between the tone-oscillator output: circuit I18 and the limiting amplifier-- input circuit I15. Normally, the shunt arm' iSII. of the attenuator I19 is shorted out by means-of the 13-2 armature and associated bacle contact of the transfer relay B.. This leaves a highresistance comprisingthe series arm IS-I of the attenuator, bridgedacross the input circuit I15 to the limiting amplifier during speech transmission periods, but this does not affect. the circuit operation, due to-the negligible attenuation thus produced. When, however, the transfer 13 is energized as explained below, the shortthrough its B4 contacts is removed'and the dial tone circuit I18 is thusconnectedthroug-h the'attenuator-HS and over cir* cuits I13, I15 tothe operators switchboard jacks I65, I66. The level of this dial tone transmitted to the switchboard jacks, can be adjusted by means of thevariable shunt arm 166 of the attenuator I19. Also, and as above pointed out, when the B relay is energized the dial tone. is transmitted-from circuit I18 through the B-I contacts ofthe B relay to-the land-based transmitterovercircuits I11, I63.

During normal .talkingperiods, voice. frequency componentswhich are to be transmitted tothe land-based. transmitter, either through the switchboardjacks I65,v i56 or from one of the land-based receiver. circuits N50, I6I, are applied to the limiting amplifieninput circuit I15, via cir.- suit] 13., which limiting amplifier llllis, as above explained; normally connected: through its. out-. put circuit 116. and the Bel -baclr'contact and armature of the B relay, totheland-based tranc mitter circuit, I63 viaits input circuit I11; The circuitandoperationof the limiting amplifier is, reterring. now to-Fig. 11, as-followsc The. speech input i to the. limiting amplifier is, applied over. its

input circuit I15, to the primary winding of an audio frequencyinput transformer 132, 13118650:- ondany of" which is connected between the 0011: trol gridl 83 andcathode I 84, of: a variabletransconductance. amplifier tube. I85, suchias a; 68G? 15 tube, through a volume-adjusting network I86, comprising serially connected resistors I 31, I 38, across the lower of which is bridged a volume control I89, the adjustable arm I90 of which is connected through a grid blocking condenser I 9| to the control grid I83. The speech input voltage appearing across the secondary of transformer I82, and across resistors I61, I88, is also impressed,

over connections I92, I93, between the control grid I94 and cathode I95 of one section of a twintriode tube I96 such as a BSL'I wherein it is amplified and fed thence to the other half of this tube, which is connected as a diode. To this end, the anode I91 of the first section of tube I96 is connected to a source of +3 or plate voltage over connection I98 through a load resistance I99, and is also connected through a blocking condenser 20!] and resistance 20! to the cathode 202 of the second half of tube I96, the grid 203 and anode 204 of which are connected together over connection 205. A grid condenser and leak resist ance in shunt 206 are connected between the grid 203 and the cathode 202 of the diode section of the tube, through a plate current grid biasing resistor 201 for the first half of the tube, and thence through a high resistance 2% interconnecting the cathodes I95 and 202. The rectified output of the diode, which is a negative direct current voltage of varying amplitude is fed back from the grid 203 of the diode over connection 209, to the grid'I83 of the variable trans-conductance tube I85, through a grid leak resistance 2 I 0, the latter connected in series with a blocking condenser H I, between the grid and cathode of the variable trans-conductance tube I85. The resulting output of the limiting amplifier is fed thence through an output transformer 2| 2 to the limiting amplifier output circuit I16, to which end the primary of transformer 2 I2 is connected between the anode of the tube I85 and the plate supply voltage I98, while the secondary is connected in the output circuit I16. As is also shown in Fig. 11, with reference to Fig. 9, the limiting amplifier output circuit I16 is connected to the land transmitter input circuit I11 through the B-I armature and back contacts of the B relay. Likewise, Fig. 11 shows the attenuator I19 bridged between the limiting amplifier input circuit I15 and the land transmitter input circuit I11, the latter through the B-I back contact and armature of the B relay, the shunt arm I80 of the attenuator being normally shorted by the 13-2 back contact and armature of the B relay.

Figure 11a shows the limiting action of the Fig. 11 amplifier at 1000 cycles. It can be seen from this graph that a reasonably constant output of i decibel is obtained over approximately a 30-decibel input range. The volume control I81-I90 of the amplifier input makes it possible to shift this range of regulation in such manner that it will coincide with the input levels normally encountered at this point.

Reverting to Figs. 9 and 10, a tone oscillator of panel I5I or I54 is connected to the system only during the initial dialing period of an outgoing call. The control terminal, as shown in Figs. 9 and 10, is so designed that it can be operated, as above stated, with several types of selector systems. Thus it can be operated with the Western Electric Companys 106A selectors in the mobile units, and the corresponding- Western Electric J-68311A-1 oscillator in the control terminal, per oscillator panel I54. It can also be operated with selectors in the mobile units in accordance with my applications aforesaid, and in conjunction with the oscillator of control panel I5I, the complete circuit diagram of which is as above explained, shown in Fig. 12. Also the control terminal may be used to operate in a mixed system, i. e., one in which part of the mobile units are equipped with the Western Electric 106A selectors, while other mobile units are equipped with station selectors in accordance with my applications aforesaid. In the latter case, both types of tone oscillators, per panels I5I and I54, must be provided at the control terminal. In the case where a mixed system is operated, the selection between the different groups of mobile units and the corresponding, appropriate tone oscillators per panels I5I and I54, is effected automatically by plugging into diiferent jacks I65 and I66 on the operator's switchboard I64. It will be observed that the voice circuits for these jacks, i. e., the tip and sleeve conductors, respectively, are connected in multiple to the voice circuit I15, but that one of these jacks has an additional contact 2, which operates a system selection relay X when the operator inserts the plug 2I4 of her cord circuit 2I5 into jack I66. This circuit is traced from battery 2I2a through the winding of relay X, and over connection 2I8 to ground, through contacts 2II of jack I66. The system selection relay is provided with a pair of contacts X-I, which normally connect the dialing circuit I18 through the X-I armatures and back contacts to the dial tone output circuit 2 I3 of the Western Electric Company oscillator panel I54, and which connects, through its armatures and front contacts, the dialing circuit I18 with the dial tone output circuit 2I6 of the oscillator panel I5I. Accordingly, if the operator inserts her cord plug 2I4 in jack I65, dial tone will be supplied from the Western Electric Company oscillator to the dial tone output circuit I18, through the X-I armatures and back contacts of the X relay; whereas, if the operator inserts her cord plug into jack I66, the X relay will operate to transfer the dialing circuit I18 to the dial tone oscillator of panel I5I. The X relay is provided with a second set of contacts X 2, which likewise transfers the dialing lead 2I1 from one oscillator circuit to the other, as explained hereinafter.

The Western Electric type J-68311A-1 oscillator of panel l54, Fig. 9, will not be described in detail in this application, as its construction and operation is well known, and per se it forms no part of the present invention. The fundamentals of the oscillator are sufiiciently shown in Fig. 9 for purposes of the present invention. It comprises two oscillators I55 and I56, the one being normally connected through the P-I front contact and armature of the pulsing relay P, and thence'through an output transformer 2 I 9 to the output circuit 2 I 3; and the other being similarly connected to the output circuit 2| 3 through-the P-I back contact and armature of thepulsing relay P. Thus fundamentally the Western Electric Company oscillator is operating continuously to connect either oscillator I55 or oscillator I56 to the output circuit. Oscillator I55 has a frequency of 600 C. P. S., which is thus normally applied to the output circuit, while oscillator I56 has a frequency of 1500 C. P. S. Operation of the pulsing relay P, in accordance with dialing impulses, as described below, switches the output circuit 2 I3 alternately from 600 C. P. S. oscillator I55 to the 1500 C. P. S. oscillator I56, for dialing stations equipped with Western Electric Company 106-A type of selector.

crimes The oscillator circuit of panel 151 employed for dialing mobile stations equipped with station selectors in accordance with my application aforesaid, according to which station selection is effected by interruption of a single dialing tone, is shown in Fig. 12, to which reference is now made. Referring to Fig. 12 the oscillator unit per se, 22 t, comprises a pair of electronic triodes 221, 22-2, connected in push-pull relation, the grid of each tube being capacitively connected to the anode of the opposite tube over connections 223, 224 containing condensers225, 226, the grids being also connected to the oathodes of the tubes in common throughindividual resistors 22?, 228, and the common biasing .resistor 22d, these resistors also being connected over a connection 230 to a common round at 246.

The oscillator circuit is energized from a power pack 24? of conventional design, energized from a 110 volt A. C. power supply connected to terminals 2&2 and thence through a switch 243 to the primary of a power transformer 244, having connected thereto in conventional fashion a full wave rectifier tube 245, which supplies the anode or plus B voltage through a filter circuit 246, to connections 2 and 2A8, extending respectively to the limiting amplifier of Fig. 11, and to the oscillator circuit of Fig. 12. The filter output 245 is shunted by a VR150 tube 2 39 for purposes of voltage regulation. The filaments of the various tubes in the oscillator circuit and also those of the limiting amplifier are supplied with 6 volts A. C. over connections 250, supplied from the low voltage secondary winding 251 of the power transformer 2441. The anode voltage is supplied over connections 2 58 to the anodes of the oscillator tubes 221, 222, through the resistors 252, 253.

The oscillator circuit 220 is designed to provide a dial tone of 2600 C. P. S., the .dial tone output voltage of which is delivered across condenser 254, to a high-Q tuned circuit 255, comprising a fixed condenser and variable inductance in parallel as shown. The output of this circuit is in turn applied through a transformer 256 and through a volume control 25! to the grid circuit of a triode power amplifier tube 258, the output of which is in turn applied through a line-matching output transformer 259, to the oscillator output circuit 216.

It will be noted that the grid of the power amplifier 258 is normally grounded through the PR-I back contact and armature of the pulsing relay PR; and that the pulsing relay in turn, is energizable from battery 212 through the X-l back contact and armature of the transfer relay X. The transfer relay X, is in turn energized, as above explained, from battery 212 over connection 218, extending to ground through the normally open contacts 21 l of jack 166 at the switchboard, Fig. 9. Thus the transfer relay X must be energized by the operator plugging her cordplug 224 into jack 166, Fig. 9, in order to connect the output of the oscillator 216 to the dialing circuit 118, Figs. 9 and 12. Accordingly, if the oscillator circuit of Fig. 12 is employed exclusively for station selection, the transfer relay must either be energized at all times, as by permanently grounding connection 218, Fig. 9, or by wedging up the X! armature of the X relay against its back contact.

Referring particularly to Fig. 12, the grid of the amplifier tube 258 is as shown, normally grounded through the PR-l back contact and armature of the pulsing relay PR. As explained below, this relay is energized just prior to the and thence to ground over connection 2H.

dialing operation, from battery 212 to ground through the X contactof the transfer relay 0,

eration of the pulsing relay PR in turn connects ground to the slow release relay SR, Fig. 12, which holds up during dialing pulses. I As noted below this slow release relay SR is required only where the Western Electric oscillator panel 154 is required in addition to panel 451 Fig. 9 for-dialing mobile stations in a Western Electric G2 terminal and to provide the same circuit criteria as does the Western Electric J-683-11A-1 oscillator panel 1 54.

Reverting to Figs. -9 and 10, which show the wiring diagram for the overall system layout,

it -will be noted that circuit which extends from the operators switchboard jacks 1 65, 166 terminates in two serially connected primary windings, 2 65, 266 -of transformer T-l, which are interconnected at their midpointsby a condenser 26], transformer winding 265 being also connected at its midpoint through a relay .PA, to ground, and winding 2% beingalso connected .at its midpoint through a relay PB to battery. Transformer T-l also includes a singlesecondary Winding 2 63 which is connected across circuit 113, extending as above explained .to .the voice output circuits M1, 112 of th incoming land- -based receivercircuits liiil, lel, circuit H3, being also connected to the limiting amplifier input circuit 1'15. As-abovenoted, under normal speech transmission conditions, one high impedance series'element i131 of the T-pad attenuator H9,

is bridged across circuit F13, the parallel branch 18E] of the T-pad being normally shorted by the 13-2 contacts of the transfer relay B. Also as above explained the output 1'16 of the limiting amplifier, .is normally connected to the equip- .ment side of the transmitter line panel through the B-1 .back contact and armature of the B relay. vDuring dialing periods, the transmitter relay B connects the equipment side of the transmitter line panel to one of the dial tone oscillators over circuit 1'58; and in addition it removes the B-2 contact short across the parallel branch 189 of the T-pad attenuator i113. This applies dial tone from the tone oscillator output circuit 18 to the outgoing land-based transmitter circuit 163, and also through the T-pad attenuator 1'19 to circuits Il3and 1'15 extending to the operators switchboard jacks 65, E66. At the end of the dialing period, release of the B relay restores all circuits to the condition above described.

In addition to the voice circuits above described, the following signaling circuits exist between the control panel, and the various other panels above mentioned.

(a) A Codan relay connection'Zslii extends from the L-2 contacts of the L relay in the receiver line panel, to the winding of the line relay LR in the control panel. Referring momentarily to Fig. 6 in conjunction with Fig. 9, it will be recalled from the above that the operation of the land-based receiver Codan relay, such as C-l, on incoming calls operates the L relay, Figs. 6 and 9, on the control terminal, receiver line panel, thereby connecting ground to lead Zlil through the L-2 contacts of the L relay. This in turn operates the line relay LR in the control panel to light the line lamp Iii-l on the operators switchboard, 54,318 explained more fully below.

(b) A transmitter control connection 211 extends from the upper contact of switch 5-2 on the transmitter line panel to the TR-1 armature of a transmitter relay TR on the control panel.

It will be noted that the front Thy-l contact of the TR relay is connected to battery 2112, so that when the IR relay operates it connects battery over lead 201% and through winding 26 of transformer M2 on the transmitter line panel and thence over conductor fill of the land-based transmitter circuit 63 to ground through the LL relay, referring now to Fig. at the distant or land-based transmitter circuit I553, thus to switch on the land-based transmitter in the manner above described in connection with Fig. 5.

(c) A connection 2l3 extending from the winding of the transfer relay B on the limiting amplifier panel to the SS-I front contact of an SS .relay, Fig. ill, on the control panel.

It will be observed in this connection that the winding of relay is connected on one side to battery 2H and on the other side to the SS-I front contact, of the SS relay, the associated armature of which is grounded, so that when the SS relay operates it energizes the transfer relay B, with results as above explained. The SS relay is operated as explained below at the beginning of each dialing operation, and remains operated until the plugged into one of the switchboard jacks H35, Its, except for such periods as dialing operations are generated by actuation of the dialing equipment 2R5 in the operators cord circuit 2 i5. .1

As above noted, the dialing lead 2 ll is normally connected through the X-2 armature and back contacts of the X relay to the pulsing relayP of the Western Electric Company dial tone oscillator panel I54; but if the X relay is energized, the dialing lead is then connected through the 21-2 armature and front contact to the pulsing relay PR. of the dial tone oscillator panel I5I.

(e) A line lamp lead 2% extends from the line lamp IS? on the switchboard panel ltd to ground through contacts 290 of the technical 'operators gang switch S-3, and through the LR-Z front contact and armature of the line relay LR on the control panel. Ground is applied to this lead through the LR-Z contact of the LR relay, whenever a call is incoming from one of the landbased receivers, thus to operate the LR relay as above explained. This lights the line lamp IG'I from battery 2?? connected thereto, and to ground over lead 216 as above noted.

(1) An oh-frequency alarm connection 218 extends from the L-2 armature of the L relay on the control terminal, transmitter line panel I52, to an off-frequency alarm line lamp 219 on the switchboard panel I6 3, the opposite side of this line lamp being connected to battery 28%. Referring momentarily to Fig. 5 in connection with Fig. 9, it will be recalled from the description of Fig. 5 that when the land-based transmitter is operating, but off-frequency ground 55 is applied over lead 68 to conductor 6! of the land-based transmitter circuit I63 extending to the control terminal, and actuates the L relay on line panel I62 thereat, operation of which .connects ground 28! through the L-2 armature.

2i) and front contact of the transmitter line panel L relay, to lead 2'58, thereby to light the offfrequency alarm lamp 219 on the operators switchboard panel I64.

(g) An audio frequency connection 282 extends from the 3-! armature of the transfer relay B on the limiting amplifier panel H69 to a loud speaker 283 on the control panel, for monitoring purposes. The lead 282 is connected to the loud speaker through attenuator 284 for setting the loud speaker volume level as desired.

(h) A busy lamp connection 285 extends from the busy lamp let on the switchboard panel to ground through contacts 289 of gang switch S-3, and thence through the TR-Z front contact and armature of the transmitter relay TR. Ground is applied to this lead whenever the land-based transmitter is switched on, through the TR-2 contacts aforesaid, thus to light the busy lamp from battery 2W connected thereto.

(1') As above pointed out operation of the control terminal may be taken over by the control terminal technical operator. And this may be effected by operation of a gang switch S-3 on the control terminal which switch is normally in the position shown in Figs. 9 and 10, but twhen operated to the left in Fig. 9 connects the technical operators circuit 287 to the voice circuit Ill5, while disconnecting the switchboard jacks I65, I66 therefrom at gang switch contacts 288. Also operation of this gang switch applies ground at 289 to lead 285 thus to energize the switchboard busy lamp [66, as long as the technical operator takes over. Also operation of the gang switch to the left disconnects at its contacts 296, lead 216 extending to the switchboard line lamp I6 1, thus preventing this line lamp from being energized. On the control terminal the technical operators position is provided with line and busy lamps 29 I, 292, which are energized over the same circuits above described, as are the switchboard line and busy lamps I61, I58. Operation of the gang switch 286 also opens at its contacts 293 the circuit 218 extending to the off-frequency" switchboard alarm lamp 279.

(7') The control terminal may be equipped with a monitor receiver 294 for actuating an associated Codan relay 295 in response to transmission of carrier from the land-based transmitter, normally a connection 296 extends from ground 29? through the armature and back contact of the Codan relay 295, and through the winding of -a monitor receiver relay MR on the control panel to battery 296. Thus the monitor receiver relay MR is normally energized over circuit 2%, but becomes deenergized in response to energization of the Codan relay 295 of the monitor receiver, when the land-based transmitter is operating. When the MR relay thus releases, it also releases through its MR-I contacts the control panel line relay LR, thereby to extinguish the switchboard line lamp IG'I following operation of the TR relay as explained more fully below. If a monitor receiver 29 3 is not employed, an alternative operating circuit for the MR relay is obtained through the TR 2 contacts of the TR relay by actuating the switch arm of a switch 298 from the contact to which lead 296 is connected to a contact 299 to the back 'I'R-2 contact of the TR relay, also for purposes and as explained more fully below.

(is) The PA relay in the switchboard circuit I15 controls through its PA-I contacts the operation of the transmitter relay TR, as above noted.

The PB relay in circuit H5 is one of a sequence of relays including a vibrating ray VR and a super slow relay SS, Figs. 9 and 10, which regulate the period during which the dial tone is applied to the switchboard and land-based transmitter circuits 5, H3 for effecting the dialing and subsequent ringing of a mobile unit called, also as explained below. The EB and EA relays, Fig. 10, form part of an extra pulse circuit 300, Figs. 9 and 10, required in conjunction with the Western Electric Company oscillator circuit its, as explained below. The control terminal is equipped with an option board 3G1, Fig. 10a, provided with strapping terminals to 0-12 inc. for strapping the extra pulse circuit 300 in or out, as required, depending on whether or not some of the mobile units are equipped with the station selectors responsive to the Western Electric oscillator circuit I54, and also for providing additional strapping connections, as explained below, but for convenience the corresponding straps have been shown as switches 298, Fig. 9, and 3! 0, 3|3 and 328, Fig. 10.

The functions of the control terminal system of Figs. 9 and 10 will now be described, first with reference to incoming calls, then with reference to outgoing calls, and finally with reference to special circuits and operations incorporated therein.

Incoming caZZs.-Referring to Figs. 6, 9 and 10, when incoming carrier from a mobile station is received for example by land receiver LR-A, its Codan relay is energized to connect ground :02 through the lower winding of the FF transformer at the land receiver station and thence over conductor iii to the control terminal receiver line panel and thence through winding 45 of transformer F thereat and through the L relay to battery, thus energizing the L relay. This applies ground through its L-2 contacts to connection 210 extending to the control panel. If at the time this call is incoming, the land-based transmitter is not operating so that the transmitter relay TR is deenergized and themonitor receiver relay MR is energized as aforesaid, application of this ground to connection 270 will immediately energize the control panel line relay LR from battery 3332, through the LR relay winding and thence through the parallel paths comprising the TR-3 back contact and armature of the TR relay and the MR4 front contact and armature of the MR relay. The LR relay upon operating, will immedi ately lock up to ground through its LR-l front contact and armature, under control of the TR and MR relays as aforesaid. The LR relay upon thus energizing, applies ground through its LR-Z armature and front contact to the line lamp 29! at the technical operators position, which lights up from battery 302, and also to the switchboard line lamp itl, which lights up from battery 21?.

Nothing further happens until the operator inserts her cord plug 2M in jack I65. When this occurs, the voice circuit I15 is closed through the tip and sleeve conductors of the operators cord plug 52M and thence through the dialing equipment 2'55 bridged across the midpoints of the primary winding of transformer 355 in the operators cord circuit 265, it being understood in this connection that with the dialing equipment 2'35 in its normal position the cord circuit provides a short circuiting connection. Accordingly the PA and PB relays operate over the circuit traced from battery through the PA relay winding, transformer winding 266 and over circuit i715 through contacts 288 of switch S4 and through the operators cord circuit returning thence over circuit H5 through transformer winding 265 and the PB relay winding to ground.

"These are fast operating relays, employed in order to assure a minimum distortion of dialing pulses. Relay PA when operated, energizes the transmitter relay TR from battery 304 to ground through the PA-l front contact and armature of the PA relay. The TR relay being slow release, will remain energized during dialing pulse operations of the PA relay. The TR relay upon energizing, applies battery .212 through its TR-l front contact and armature to connection 2' extending to the control terminal, transmitter line panel and thence through switch 6-2 and the lower winding 46 of transformer 162 and over conductor as of the land-based transmitter circuit R33 to operate relay LL, Fig. 5, at the landba'sed transmitter, thereby to switch on the power supply to the transmitter LT as above explained. In addition, operation of the TR relay, opens at its TR-.3 contacts, one of the two operating paths through which the control terminal, line relay LR .is held energized through its LR-l contacts. In addition operation of the TR relay applies ground through its TR2 armature and front contact to connection 285 extending to the switchboard for energizing the switchboard busy lamp 1258 from battery 21?, while at the same time the busy lamp 292 at the technical operators position is also energized to the same ground from battery 392. Whenever an eastwest busy indication is needed, an additional relay may be connected to terminal "I -l8 of the control terminal, and thus operated over this same circuit to ground including connection 285 and the TR-2 contacts of the TR relay. Thus operation of the PA relay puts the landbased transmitter on the air.

If a monitor receiver, such as 294 is used, its Codan relay 295 is wired up in such fashion as above explained that it normally keeps the monitoring relay MR, energized, and deenergizes this relay whenever the land transmitter carrier is received, provided its frequency falls within the acceptance band of the receiver. If no monitor receiver is employed, switch 298 is actuated, as explained, to connect its switch arm to contact 299, in which event the TR2 contacts of the transmitter relay take over the function of the monitor receiver Codan relay. Actually no switch such as 298 is employed in the circuit, the connection in question being obtained by strapping terminals 0 5 and 0-6 on the option board 3M, Fig. "10a. In any event the MR relay, upon releasing over either of the circuits aforesaid, following operation of the TR relay, interrupts at its MR-l contact, the remaining holding circuit for the control terminal line relay LR, which thereupon releases and extinguishes the line lamps I67 and 291.

Insertion of the operators cord plug 214 in jack 165, also operates the PB relay over its operating circuit above traced. The PB relay upon thus operating, applies ground through the 'PB-l armature and front contact to the dialing lead 2l'i which controls the tone generated in the dial tone oscillators. As the circuit description under present consideration, applies only to the case of an incoming call, the contrdl terminal line relay LR is energized when the operator inserts her cordplug BM in the switchboard jack, so that the LR-3 armature, Fig. 10, of the LR relay is actuated against its lower or front contact, and hence the operating circuit for the vibrating relay VR, traced from battery "3B5 through the winding of this relay, the LR3 armature and back contact of 

